trixbox-2.8.0.1 can't automaticaly config openvox cards, the soluiton is :
1. run the right linux kernel(2.6.18-128.1.10.el5) when you select the grub(the default one is wrong)
2. use command " dahdi_genconf " in shell
3,. then start asterisk, run "dahdi show channels", you should see the channels in the output
